by Other » 16/04/08, 07:04
Hello
For small aviation few small engines have been developed and succeeded well (in the range of 60hp to 180Hp) I would not speak of reliability, but of the airplane / engine / propeller adaptation.
Among the most successful the Continental 90hp the lycoming 180hp
The poorly adapted and most widespread the continental 100hp, the 85 hp, the Franklin 125hp
The worst engine propeller hitch is on the Cessna 150 and it is the best-selling aircraft…
An airplane engine must have a high torque, it has a different design from an automobile,
It must turn at 2800rpm maximum, reach its maximum torque around 2300rpm, have 75% of its power at 2400 rpm be able to provide 80% of its power continuously, and if mounted on a propeller with a fixed pitch be able to fetch 100% of its nominal power in level.
Being simple, light, robust, is reliable,
This is suitable for (large) displacement engines with a camshaft that has a parure for torque and power at low speed (all the opposite of the sharp automobile engine)
Strangely we note that these are characteristics of the diesel engine
The disadvantage in auto diesel is heavy, slowed down, needs a fairly consistent steering wheel, it will seek its maximum power at speeds of 4000 rpm, which requires the manufacturer to install a reducer, which has the disadvantage of limiting the choice in the propellers.
Metal propellers with a gear reducer pose a problem on gears
Belt reducers require belt replacement every 500 hours
A reducer is also mechanical losses, the weight gain on the motor is lost in the reducer.
Another problem on car engines is all the electronic servitude which cannot be doubled for reliability, and which is less useful on constant speed engines.
In aviation reliability comes before yield and economy.
If the car manufacturers had designed a mechanical indirect injection diesel engine, which has a fairly large displacement its full power at 3000 rpm
Its maximum torque at 2000 rpm an interesting weight, it would make the ideal candidate for an airplane.
Contrary to what many people think about propellers, a variable pitch propeller, has a perfect twist only at a certain position, when the blade turns on the hub the theoretical twist varies more quickly at the tip of the blade than at the hub
It becomes unfavorable for the big step.
A variable pitch propeller is only useful for a fast plane, installing a variable pitch propeller on a Piper J3 or an ULM which has a speed of 120 km / h uphill and a speed of 160 km / h cruising is ridiculous, a propeller with fixed pitch well proportioning is also efficient.
A good propeller has a low cruising slip around 10%
It must be of sufficiently large diameter to have a speed at the end of the blade around 750kmh (the one that turns the fastest on the Cessna 180 reaches 1050 kmh at the end of the blade at takeoff) in a cruise around 800kmh.
The trend is to install propellers of small diameter, to compensate for the lack of torque of the engines, this makes a significant slip on takeoff and mounted. (case of Cessna 150)
There are several schools of thought depending on the country
In Russia it's big propellers, pale drop, square tip
In America it is large minimum propeller 1,80m to 2,15m with medium tip, square or rounded blades. Duralumin and composite
In France it is small propellers, with narrow ends, pointed or slightly rounded generally in wood or composite.
The best propellers were designed by Lucien Chauvier in the early days of aviation, almost all the propellers were taken from his designs.
Sometimes I wonder why this knowledge is lost.
Andre
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